Major Shoreline Retreat Following Snowball Earth

Neoproterozoic glacial diamictites have stimulated geological debate for almost a century. Originally providing an argument for continental drift, they now provide a debate around a frozen planet Earth. It is likely these globally pervasive deposits represent a Snowball Earth, where a runaway ice albedo allowed the oceans to freeze from pole to pole. The hypothesis demands that, in order to bring the planet back from its icy state, volcanic degassing would increase greenhouse gasses to a critical point to overcome the albedo effect. Once this occurs, the planet should shift rapidly from a snowball to a hot house, possibly, as has been proposed, within less than 2000 yrs. However, cap-carbonate rocks overlying the glacial sediments, that are typically interpreted as transgressive deposits show evidence, such as multiple magnetic reversals, indicating they accumulated instead over 100's of thousands of years. If so, sea-level rise following the glaciation would have been significantly prolonged compared to the reigning paradigm of rapid deglaciation. We discuss modern transgressive deposits and sequence stratigraphy to hypothesize that cap-carbonates represent a period that followed rapid shoreline migration landward during the demise of Snowball Earth. Progressive erosion of the continents during the lowstand sea-level transferred large masses of sediment into the oceans creating broad continental shelves. The barren, low-gradient topography that was left in the Snowball aftermath allowed shorelines to migrate uninterrupted landward for potentially 100's of kilometres during a period of rapid deglaciation. Shorelines took 100's of thousands of years to prograde back to the continental shelves, providing a sediment hiatus that allowed for the precipitation of carbonate and potentially the perfect environment for the development of complex life.